Transcript Chapter 3 - Therapeutic Range and Routes of Drug

Fundamentals of Pharmacology
for Veterinary Technicians
Chapter 3
Therapeutic Range and
Routes of Administration
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
The Therapeutic Range
• All drugs should be considered
potential poisons and should be
dispensed and given with great care
• The therapeutic range of a drug is
the drug concentration in the body
that produces the desired effect in
the animal with minimal or no signs
of toxicity
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Keeping Drugs in the
Therapeutic Range
• Three major drug factors keep drugs
in their therapeutic range:
– Route of administration
– Drug dose
– Dosage interval
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Route of Administration
• Parenteral drugs are given by a route
other than the gastrointestinal tract
• Nonparenteral drugs are given through
the gastrointestinal tract
• Factors that affect the route of drug
administration include:
– Drug causes one effect when given
parenterally and another nonparenterally
– Water-insoluble drugs can be given IM,
but not IV
– Some drugs are destroyed by stomach acid
and cannot be given orally
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Injectable Routes of
Administration
• Injectable routes are parenteral
• Most common injectable
administration routes are IV, IM, and
SQ
• Drugs given by injectable
administration routes may be
aqueous solutions or emulsions
(mixtures of two immiscible liquids)
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Injectable Routes of
Administration (IV)
• Drugs given IV have rapid onset of action,
higher initial body levels of drug, and
shorter duration of activity
• IV injection techniques include bolus
administration, intermittent therapy, and
infusion of fluid
• In most cases, IV drugs should be given
slowly
• All air bubbles must be removed from the
drug before administration to avoid
causing air emboli and tissue damage
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Injectable Routes of
Administration (IM)
• Drugs given IM have relatively rapid onset of
action and longer duration of activity than IV
drugs
• Absorption rate depends on drug formulation
• IM-injectable drugs may be in a substance that
delays absorption; these are referred to as
repository or depot preparations
• IM drugs can be in aqueous solutions or
suspensions
– Solutions are clear liquids that contain one or more
solvents and one or more solutes
– Suspensions are liquid preparations that contain solid
drug particles suspended in a suitable medium
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Injectable Routes of
Administration (SQ)
• Drugs given SQ have slower onset of action and
longer duration of activity than IV and IM drugs
• Absorption rate may be altered by the vehicle in
the preparation
• Larger amounts of solutions can be given SQ;
amount given should be based on animal species
involved
• Pellets can also be implanted into the
subcutaneous space
• The rate of absorption of SQ fluid can be
manipulated by temperature
– Applying heat to the area increases the rate of absorption
– Applying cold to the area decreases the rate of absorption
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Other Parenteral Administration
Routes
• Inhalation administration introduces drug
to the animal by having it breathe the drug
into the lungs
– Particles diffuse across the alveolar
membrane
• Topical medication goes on the surface of
skin or mucous membrane
– Forms of topical medication are summarized
in Table 3-2
• Other parenteral administration routes are
listed in Table 3-1
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Nonparenteral Administration
Routes
• Oral administration delivers the drug directly to
the animal’s gastrointestinal tract
• Before entering the bloodstream, an oral drug
must be released from the dose form, transported
across the GI tract, and passed through the liver
• Oral drugs usually have slower onset of action,
longer duration of activity, and absorption rates
that may be affected by the type of digestive tract
and/or GI disease
• Oral drugs may be tablets, capsules, boluses,
powders, solutions, suspensions, or emulsions
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Drug Dose
• The dose of a drug is the amount of drug
administered at one time to achieve the desired
effect (can be in mL, cc, mg, g, tablets, etc.)
• Loading dose: initial dose of drug given to get the
drug concentration up to the therapeutic range in
a very short period of time
• Maintenance dose: dose of drug that maintains or
keeps the drug in the therapeutic range
• Total daily dose: total amount of drug delivered in
24 hours
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Drug Dosage
• The dosage of a drug is the amount of
drug per animal species’ body weight or
measure
– Examples include mg/kg or g/lb
• Dosage interval: how frequently the
dosage is given
– Examples include BID or TID
• Dosage regimen: dosage interval and the
dosage together
– Examples include 30 mg/kg TID and 5 g/lb
BID
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Drug Toxicity
• Drug toxicity may be due to human error
and/or accident
• Drug toxicity may be related to side effects
of the drug
• Examples of drug toxicities:
–
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–
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Outright overdose
Relative overdose
Side effects
Accidental exposure
Interaction with other drugs
Incorrect treatment
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.
Counteracting Drug Toxicities
• Veterinary staff must act quickly to
counteract any problems caused by drug
treatment
• Some ways to treat drug toxicities:
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Removal of the offending drug
Enhancing drug removal by the animal
Counteracting with an antidote
Providing symptomatic care or nursing care
until the toxicity signs have diminished
© 2004 by Thomson Delmar Learning, a part of the Thomson Corporation.